Cystoid macular edema (CME), a common complication of cataract surgery, manifests as leakage of plasma from the perifoveal capillar- ies, formation of macular cystoid spaces, and marked visual impairment [1, 2]. The disease may or may not resolve spontaneously, and vit- rectomy leads to successful resolution of the edema in some patients with CME. Fluorescein angiograms and OCT images of a patient with typical CME before and after vitrectomy are shown in Fig. 4.4. The fluorescein angiogram (Fig. 4.4A) shows extensive fluorescein leakage from the macular capillaries, and OCT reveals multiple cystic spaces in the macula before surgery. After vitrectomy, fluorescein leakage
is not present (Fig. 4.4B), and the macular configuration evaluated by OCT returns to normal.
Although CME may be associated with several retinal diseases, aphakic and pseudo- phakic CMEs are good models for studying the principle of the pathophysiology of CME. This is because, unlike the CME in diabetic retin- opathy or central retinal vein occlusion, there are few background abnormalities such as ischemia or damaged RPE. Thus, the patho- physiology may be relatively simple to analyze.
The interpretations may then be extended to analysis of more complex CME, such as that seen with diabetic retinopathy.
4.2 Aphakic or Pseudophakic Cystoid Macular Edema
Fig. 4.4. Fluorescein angiograms and OCT images obtained before (A) and after (B) vitrectomy from a 72-year-old man with pseudophakic cystoid macular edema (CME)
The focal macular ERGs in the affected eyes of patients with aphakic or pseudophakic CME without systemic disease may be classified into three types (Fig. 4.5) [3]. In type 1, the ampli- tudes of the OPs are reduced compared to that of the normal fellow eye, but the amplitudes of the a-waves and b-waves are nearly normal. In type 2, the amplitude of the OPs and b-waves are reduced, but the a-wave is normal; and in type 3 the amplitude of the OPs, a-waves, and b-waves are reduced.
The distribution of the best-corrected visual acuity for each type of CME is shown in Fig. 4.6.
The difference in visual acuity between types 1 and 3 is statistically significant.
Fluorescein angiograms and focal macular ERGs in eyes with CME and after the resolution of CME are illustrated for three representative cases in Figs. 4.7 to 4.9. Case 1 (Fig. 4.7) was a 51-year-old man who had had cataract surgery on his right eye with implantation of a poste- rior chamber lens. His preoperative visual acuity of 0.1 improved to 0.9 postoperatively but then gradually decreased to 0.6 five months later. Fluorescein angiography disclosed CME in the right eye. The OPs of the focal macular ERGs were selectively reduced (type 1) com- pared with that of the normal fellow eye. Six months later the CME resolved spontaneously, and fluorescein angiography disclosed a
4.2.1 Focal Macular ERGs
Fig. 4.5. Focal macular ERGs recorded from representa- tive patients with types 1, 2, and 3 pseudophakic CME.The stimulus spot was 10° in diameter. (From Miyake et al. [3], with permission)
Fig. 4.6. Distribution of best-corrected visual acuity in patients with types 1, 2, and 3 aphakic or pseudophakic CME. The differ- ence between types 1 and 3 is statistically significant (P= 0.0072). (From Miyake et al.
[3], with permission)
normal pattern with no leakage; the visual acuity improved to 1.2. The focal macular ERGs returned to normal levels, with the amplitudes of the OPs comparable to those recorded from the fellow eye.
Case 2 (Fig. 4.8) was a 70-year-old woman who visited our hospital 14 months after cataract surgery with implantation of a poste- rior chamber lens in her right eye. Her visual acuity was 0.2, and CME was detected with fluorescein angiography. The focal macular ERG had a type 2 pattern, with normal a-waves and reduced b-waves and OPs. Because vitreous was incarcerated by the iris, pars plana vitrec- tomy was performed to separate the vitreous from the iris. Five months after vitrectomy her visual acuity had improved to 0.7, and the CME was no longer present (seen by fluorescein angiography). The focal macular ERG recov- ered to the type 1 pattern in which only the OPs were reduced. Thus, the focal macular ERGs changed from type 2 to type 1 after resolution of the CME by vitrectomy.
Case 3 (Fig. 4.9) was a 60-year-old man who was examined after bilateral intracapsular cataract extraction 16 and 20 months earlier.
Fluorescein angiography disclosed CME in the right eye. The focal macular ERGs had a type 3 pattern with reduced a-wave, b-wave, and OP amplitudes. Careful examination showed that vitreous was incarcerated in the corneoscleral wound, and the pupil was distorted. Pars plana vitrectomy was performed to detach the vitreous from the wound to restore the shape of the pupil. Four months after vitrectomy, his visual acuity was 0.3, and fluorescein angiogra- phy disclosed less severe CME. The focal macular ERGs recorded 4 months after vitrec- tomy had a type 2 pattern; that is, the a-wave amplitude recovered almost to the level seen in the fellow eye, but the b-wave and OP ampli- tude remained smaller than that in the normal eye.
With aphakic or pseudophakic CME, the amplitudes of the OPs are reduced and the implicit times are delayed regardless of the
Fig. 4.7. Case 1. Focal macular ERGs (left) and fluorescein angiograms (right) when CME is present (top) and resolved (bottom). After spon- taneous resolution of the CME, the focal macular ERG recovered from type 1 (top) reverts to normal (bottom).
(From Miyake et al. [3], with permission)
visual acuity. These findings suggest that OPs are the most sensitive indicator of CME.
The progressive increase in the severity of CME is manifested by a decrease in the b-wave
followed by a reduction of the a-wave. There- fore, analysis of each component of the focal macular ERG can be used to quantify the sever- ity of CME [3].
Fig. 4.8. Case 2. Focal macular ERGs (left) and fluorescein angiograms (right) before vitrectomy (top) and 5 months after vitrectomy (bottom).
After resolution of the CME by vitrectomy, the focal macular ERG recovered from type 2 to type 1.
(From Miyake et al. [3], with permission)
Fig. 4.9. Case 3. Focal macular ERGs (left) and fluorescein angiogram (right) recorded before vitrectomy (top) and 4 months after vitrectomy (bottom). After resolution of the CME, the focal macular ERG changed from type 3 to type 2.
(From Miyake et al. [3], with permission)
It is conceivable that the full-field ERGs may be within the normal limits in cases of simple aphakic or pseudophakic CME without an associated systemic disease such as diabetes.
This is true because the abnormal fundus and fluorescein angiographic findings are limited to the macula or within the posterior pole. The full-field ERGs should be normal because the peripheral retina contributes more significantly than the macula to the full-field ERGs. However, our study of full-field ERGs showed that, although there were no significant differences in the amplitudes and implicit times of the a- waves and b-waves between the affected eyes and the fellow eyes without CME, the ampli- tudes of OPs were significantly reduced in the affected eyes [4] (Figs. 4.10, 4.11). The degree of reduction of the OPs was strongly correlated with visual acuity (Fig. 4.12), and the mean implicit time of the first OP was significantly
delayed in the affected eyes. The abnormal OPs of the full-field ERGs indicated that the abnor- mality was not limited to the macula but had spread over the entire retina.
What do these findings mean? Chemical mediators are biosynthesized at the site of the primary lesion in various diseases, and it has been postulated that they diffuse into the vitre- ous and cause macular edema postoperatively [5]. Why do the chemical mediators act only on the macula and not on other parts of the retina or eye? The results of full-field ERG suggest that, even without a visible vasculopathy, as in diabetic retinopathy, the inflammatory chemi- cal mediators do affect the retinal vessels over a large area of the retina in the presence of aphakic or pseudoaphakic CME. This suggests that CME is only one manifestation of a more diffuse intraocular pathological alteration.
4.2.2 Full-field ERGs
Fig. 4.10. Mixed rod–
cone (bright flash) ERGs recorded from eight representative eyes with pseudophakic CME and normal fellow eyes. The OPs, recorded with a short time constant (0.003 s), are shown below the regular ERGs and are markedly smaller in the affected eyes. (From Terasaki et al.
[4], with permission)
References
1. Irvine SR (1953) A new defined vitreous syndrome following cataract surgery: interpreted according to recent concepts of the structure of the vitreous. Am J Ophthalmol 36:599–619
2. Gass JDM, Norton EWD (1966) Cystoid macular edema and papilledema following catarct extrac- tion; a fluorescein funduscopic and angiographic study. Arch Ophthalmol 76:646–661
3. Miyake Y, Miyake K, Shiroyama N (1993) Classification of aphakic cystoid macular edema
with focal macular electroretinograms. Am J Ophthalmol 116:576–583
4. Terasaki H, Miyake K, Miyake Y (2003) Reduced oscillatory potentials of the full-field electroretino- gram of eyes with aphakic or pseudophakic cystoid macular edema. Am J Ophthalmol 135:477–482 5. Miyake K (1995) Cystoid macular edema as part of
diffuse intraocular symptoms. Folia Ophthalmol Jpn 46:219–231
Fig. 4.11. Left: Summated amplitude of the OPs of the full-field mixed rod–cone ERGs recorded from the affected eyes (ordinate) and the normal fellow eye (abscissa). Right:
Implicit time of OP1 recorded from the affected eyes (ordinate) and fellow eyes (abscissa). Normal values for the total amplitudes of OPs and implicit time of OP1 are indicated by shaded backgrounds. (From Terasaki et al. [4], with permission)
Fig. 4.12. Relation between the best-corrected visual acuity (log MAR units) and the ratio of the full-field total OP amplitudes of the affected eyes to normal fellow eyes. A significant correla- tion was found between visual acuity and total OP amplitude.
(From Terasaki et al. [4], with permission)
